Metadiscourse is a new and interesting field of inquiry which is believed to play a vital role in organizing and producing persuasive writing, based on the norms and expectations of people involved. Metadiscourse embodies the idea that writing and speaking are more than just the communication of ideas and presentation of ideational meaning. Rather they are considered as social acts which involve writers, readers, speakers and listeners to interact with each other to affect the ways ideas are presented and understood. Metadiscourse is, therefore, believed to be an important feature of communication because we need to asses the readers' or listeners' resources for understanding the text and their likely responses to it in order to be able to write or to speak effectively. This article intends to study first, the definitions and issues of metadiscourse and then to introduce different metadiscourse signals and categorizations and examine the factors affecting their use, and finally to discuss metadiscourse in the classroom to demonstrate its values and implications for English teachers.